Method and system for mammalian joint resurfacing

ABSTRACT

A method and system for the creation or modification of the wear surface of orthopedic joints, involving the preparation and use of one or more partially or fully preformed and procured components, adapted for insertion and placement into the body and at the joint site. In a preferred embodiment, component(s) can be partially cured and generally formed ex vivo and further and further formed in vivo at the joint site to enhance conformance and improve long term performance. In another embodiment, a preformed balloon or composite material can be inserted into the joint site and filled with a flowable biomaterial in situ to conform to the joint site. In yet another embodiment, the preformed component(s) can be fully cured and formed ex vivo and optionally further fitted and secured at the joint site. Preformed components can be sufficiently pliant to permit insertion through a minimally invasive portal, yet resilient enough to substantially assume, or tend towards, the desired form in vivo with additional forming there as needed.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of an internationalpatent application filed Aug. 28, 2001 and assigned Ser. No.PCT/US01/41908 which application has not yet been published and whichitself is a continuation-in-part of Provisional U.S. Application SerialNo. 60/228,444, filed Aug. 28, 2000, the entire disclosures of which areincorporated herein by reference.

TECHNICAL FIELD

[0002] In one aspect, this invention relates to biomaterials formed exvivo for implantation and use within the body. In another aspect, theinvention relates to in situ curable biomaterials. In yet anotheraspect, this invention further relates to the field of orthopedicimplants and prostheses, and more particularly, for implantablematerials for use in orthopedic joints.

BACKGROUND OF THE INVENTION

[0003] Applicant has previously described, inter alia, prostheticimplants formed of biomaterials that can be delivered and finally curedin situ, e.g., using minimally invasive techniques. See for instance,U.S. Pat. Nos. 5,556,429, 5,795,353, 5,888,220, 6,079,868, 6,140,452,6,224,630 and 6,248,131 as well as published International ApplicationNos. WO 95/30388 and WO 97/26847 and International ApplicationPCT/US97/20874 filed Nov. 14, 1997 (the disclosures of each of which areincorporated herein by reference). Certain of these applicationsdescribe, inter alia, the formation of a prosthetic nucleus within anintervertebral disc by a method that includes, for instance, the stepsof inserting a collapsed mold apparatus (which in a preferred embodimentis described as a “balloon”) through a cannula that is itself positionedthrough an opening within the annulus, and filling the balloon with aflowable biomaterial that is adapted to finally cure in situ and providea permanent disc replacement. See also, Applicant's “Porous Biomaterialand Biopolymer Resurfacing System” (PCT/US99/10004), as well as“Implantable Tissue Repair Device (PCT/US99/11740), and “Static Mixer”(PCT/US99/04407) applications.

[0004] See also, U.S. Pat. Nos. 3,030,951 (Mandarino), 4,203,444(Bonnell et al.), 4,456,745 (Rajan), 4,463,141 (Robinson), 4,476,293(Robinson), 4,477,604 (Oechsle, III), 4,647,643 (Zdrahala), 4,651,736(Sanders), 4,722,948 (Sanderson), 4,743,632 (Marinovic et al.),4,772,287 (Ray et al.), 4,808,691 (Konig et al.), 4,880,610 (Constanz),4,873,308 (Coury et al.), 4,969,888 (Scholten et al.), 5,007,940 (Berg),5,067,964 (Richmond et al.), 5,082,803 (Sumita), 5,108,404 (Scholten etal.), 5,109,077 (Wick), 5,143,942 (Brown), 5,166,115 (Brown), 5,254,662(Szycher et al.), 5,278,201 (Dunn et al.), 5,525,418 (Hashimoto et al.),5,624,463 (Stone et al.), 6,206,927 (Fell), and EP 0 353 936 (CedarSurgical), EP 0 505 634 A1 (Kyocera Corporation), EP 0 521 573(Industrial Res.), and FR 2 639 823 (Garcia), WO 93/11723 (RegenCorporation), WO 9531946 (Milner), WO 9531948 (Kuslich).

[0005] Applicant's PCT Application No. PCT/US97/00457 (WO 9726847A1)includes the optional use of a mold, such as a balloon, and describesthe manner in which “[t]he mold created within the joint is preferablyof sufficient shape and dimensions to allow the resulting curedbiomaterial to replace or mimic the structure and function of theremoved fibrocartilage. The mold can be formed of synthetic and/ornatural materials, including those that are provided exogenously andthose provided by the remaining natural tissues. The mold can either beremoved from the site, upon curing of the biomaterial, or issufficiently biocompatible to allow it to remain in position.”

[0006] Applicant's later PCT Application No. PCT/US97/20874 (WO9820939A2) further describes the manner in which “‘mold’ will refer tothe portion or portions of an apparatus of the invention used toreceive, constrain, shape and/or retain a flowable biomaterial in thecourse of delivering and curing the biomaterial in situ. A mold mayinclude or rely upon natural tissues (such as the annular shell of anintervertebral disc) for at least a portion of its structure,conformation or function. The mold, in turn, is responsible, at least inpart, for determining the position and final dimensions of the curedprosthetic implant. As such, its dimensions and other physicalcharacteristics can be predetermined to provide an optimal combinationof such properties as the ability to be delivered to a site usingminimally invasive means, filled with biomaterial, and optionally, thenremain in place as or at the interface between cured biomaterial andnatural tissue. In a particularly preferred embodiment the mold materialcan itself become integral to the body of the cured biomaterial.”

[0007] Applicant's own use of such mold apparatuses to date hasconcentrated largely on the use of thin, extensible balloons adapted tobe positioned and then filled in situ with curable biomaterial, withparticular use as a replacement for the intervertebral disc followingmicrodiscetomy. In turn, there has been considerably less focus, todate, on the use of any such molds in other joints, such as the knee.FIGS. 6 and 7 of Applicant's PCT Publication No. WO 920939 A2, forinstance, shows a balloon and corresponding drilling template for use inknee surgery, the balloon having foot portions protruding from agenerally ovoid inflatable portion.

[0008] Finally, U.S. Pat. No. 6,206,927 describes a self-centeringmeniscal prosthesis device suitable for minimally invasive, surgicalimplantation into the cavity between a femoral condyle and thecorresponding tibial plateau is composed of a hard, high modulusmaterial shaped such that the contour of the device and the naturalarticulation of the knee exerts a restoring force on the free-floatingdevice. In what appears to be a related manner, Sulzer has introduced aunicompartmental interpositional spacer to treat osteoarthritis in theknee. See “Little Device Could Pack a Big Punch”, Sulzer Medica JournalEdition Feb. 2000(www.sulzermedica.com/media/smj-full-tex/2000/0002-full-text-6.html).The device is described as a metallic kidney-shaped insert which fillsin for the damaged cartilage between the femur and the tibia.

[0009] Such a metallic device, as described in either the Fell patentand/or Sulzer's product literature, is described as appropriate for usein younger patients with moderate to severe chondromalacia, particularlysince the product provides a hard, self-centering meniscal device thatis “devoid of physical means that fix its location”. In so doing, thedevice of Fell et al. tends to require a significant amount of intactcartilage and meniscus. Applicant's own products to date, includingthose improved embodiments described herein, have been largely gearedtoward more elderly patients, where such healthy cartilage is lacking.In turn, Applicant's devices tend to provide angular correction andimproved anchoring of the implant at the joint surface.

[0010] In spite of developments to date, there remains a need for ajoint prosthesis system that provides an optimal combination ofproperties such as ease of preparation and use, and performance withinthe body.

BRIEF DESCRIPTION OF THE DRAWING

[0011] In the Drawing:

[0012]FIG. 1 shows top and side perspectives of a preferred preformedknee implant prepared according to the present invention.

[0013]FIG. 2 shows an embodiment in which preformed components adaptedto be inserted and assembled in situ.

[0014]FIG. 3 shows an alternative embodiment in which preformedcomponents are employed.

[0015]FIGS. 4 and 5 show an embodiment in which a substantially open(saucer-shaped) mold is inserted into the joint site, to be filled witha corresponding curable biomateral in situ.

[0016]FIG. 6 shows a variety of alternative embodiments that include oneor more preformed component.

[0017]FIG. 7 shows a variety of alternative means for anchoring apreformed component such as that shown in FIG. 6d.

[0018]FIG. 8 shows a further variety for anchoring or stabilizing apreformed portion by the use of ancillary portions and/or surfacetexture.

[0019]FIG. 9 shows a variety of embodiments in a substantially closed(balloon like) mold is adapted to be inserted into the joint site andfilled with a corresponding curable biomaterial.

[0020]FIG. 10 shows a mold adapted for use as an acetabular mold inconnection with the replacement of the articulating surface in a hip.

[0021]FIG. 11 shows a patella femoral joint form suitable for use incombination with the method and system of this invention.

SUMMARY OF THE INVENTION

[0022] The present invention provides a method and system for thecreation or modification of the wear surface of orthopedic joints, andparticularly articulating joints such as the knee. In one preferredembodiment, the method relies, at least in part, upon the manner inwhich the various stages of curing a curable biomaterial, and in turn,the various stages of forming a component from the cured or curingbiomaterial, can be correlated and optimized in a desired manner. Inturn, such a method provides the ability to both generally andspecifically form the component for use in situ.

[0023] The present invention includes a variety of embodiments, each ofwhich preferably includes one or more components that are formed exvivo, and that are adapted to be inserted and finally formed orassembled in situ in order to provide a final prosthesis andarticulating joint surface. Examples of the various embodiments include,for instance,

[0024] 1) one or more components that are each partially molded ex vivo,in a manner that permits the component to be inserted and finally formedin situ,

[0025] 2) a plurality of preformed components adapted to be assembled insitu, for instance in an overlapping or interlocking fashion,

[0026] 3) an insertable open (e.g., saucer shaped) mold, adapted to beinserted and positioned within the joint site, and there used incombination with a flowable biomaterial adapted to be delivered to theopen mold in situ, under conditions that permit the flowable biomaterialto cure in contact and/or combination with the mold in order to form afinal prosthesis,

[0027] 4) one or more generally extensible envelope (e.g., balloon-type)molds, adapted to be positioned and filled in situ with correspondingcurable biomaterials, one or more of the molds themselves providing oneor more regions of generally non-extensible, preformed material. In oneembodiment, for instance, a plurality of such envelope portions (e.g., abi-compartmental single envelope) can be adapted for use on both themedial and lateral tibial surfaces, respectively.

[0028] By the selection and use of a suitable biomaterial, and otherfeatures as described herein, the present invention provides an optimalcombination of benefits, as compared to methods previously described.Such benefits include those that arise in the course of preparation andstorage (e.g., sterility, storage stability), those that arise in thesurgical field itself (e.g., ease of use, adaptability, predictability),and those that arise in the course of long term use within the body(e.g., biocompatibility, moisture cure characteristics, tissue congruityand conformability, retention, wear characteristics, andphysical-mechanical properties).

[0029] In one preferred embodiment, the method and system involve thepreparation and use of partially cured components that can be formedoutside the body, for insertion and placement into the body, and thatcan then be further formed within the joint site in order to enhanceconformance. The ability to finally form one or more components in situprovides various additional benefits, such as increased control over theoverall size and shape of the final prosthesis, improved shape andcompliance of the surface apposing natural bone, and finally, improvedshape and compliance of the opposite, articulating surface.

[0030] As used herein, the word “cure”, and inflections thereof, willrefer to the extent to which a curable biomaterial, as used to form acomponent of this invention, has begun or completed whateverphysical-chemical reactions may be contemplated in the course of fullyforming the component, at the surgical site, for long term use in situ.In turn, the biomaterial can be considered as uncured (as in componentparts that have not yet been mixed or compositions that have not yetbeen activated), or it can be partially cured (e.g., wherein thecomponents have been mixed, or compositions activated, under conditionssuitable to begin the curing process), or it can be fully cured (e.g.,in which case, whatever chemical reactions may have occurred havesubstantially subsided). Generally, uncured compositions are sterile,storage stable, and often flowable, though are typically not yet formedor capable of being formed.

[0031] Curing compositions, by contrast, generally begin as flowablecompositions, but become nonflowable over a finite time period as theybegin to gel or set. Curing compositions can also be minimally formed,e.g., outside the body by the use of molds and/or suitable shapingtools, and/or within the body, as by the initial positioning of thecomponent on supporting bone and by the repositioning of opposing,articulating bone surfaces. Thereafter, it is contemplated that certaincompositions of this invention can be further formed, over time, as bythe gradual effect of articulating bone in the course of long term use.

[0032] As also used herein, the word “form”, and inflections andvariations thereof, will refer to the manner and extent to which acomponent has been sized and shaped, in either a general and/or specificmanner, for use at a joint site. In turn, the forming of such acomponent can occur either ex vivo and/or in vivo, as well as in ageneral manner (e.g., by the use of an ex vivo mold or tools) and/or aspecific manner (e.g., by final curing in apposition to supporting boneand/or opposing articulating bone surfaces), as well as combinationsthereof.

[0033] A component can be “specifically” formed in this manner in orderto conform the component (and particularly its surfaces) to thecorresponding specific shapes and dimensions of bone in situ, includingboth supporting bone surfaces and/or opposing (e.g., articulating) bonesurfaces. Such specific conformation, in turn, can be used to improve avariety of characteristics of the final implant, including comfort,mechanical performance, and/or long term stability. Such conformationcan also include aspects in which one or more components, or thecomposite prosthesis, are “conformed” in correspondence with the jointsite (e.g., by final shaping and curing processes that occur in situ).

[0034] Such conformation can also include aspects in which thecomponents, or prosthesis itself, are adapted to be “deformed” withinthe site, as by the application of force. For instance, a substantiallyfully formed component can be provided to have sufficient mechanicalproperties (e.g., strength and resilience) to permit it to be insertedinto a joint site and effectively deformed under normal anatomic forcesFor instance, a substantially convex component can be deformed to assumethe corresponding concave shape in situ, in, while retaining sufficientresilient strength to tend towards its original convex shape (e.g.,analogous to the manner in which a locking washer can be deformed inuse, while tending toward its original shape). Preferably, a final kneecomponent is adapted to be deformed under conditions of use within thebody (e.g., under physiologic load), while maintaining desired size andtibial congruency, and in a manner that provides desired fit andthickness for desired angular correction.

[0035] Hence a “preformed” component will generally refer to a componentthat is at least partially formed ex vivo, as by the surgeon's selectionand use of an appropriately sized ex vivo mold. Such a preformedcomponent can be specifically formed as well, including in an ex vivofashion, as by the use of a customized mold that is itself reflective ofthe particular dimensions and contours of the intended joint site. Suchcustomized molds can be prepared, for instance, by the use of externalimaging means, and/or by the appropriate use of negative and/or positivemolds taken at the tissue site. Optionally, and preferably, thepreformed component is specifically formed, in whole or in part, bybeing positioned in situ, prior to the completion of the curing process,and in apposition to both supporting bone and opposing bone surfaces.Once positioned within the joint site, any such component or prosthesiscan be adapted to be deformed in order to improve its retention and/orperformance in situ, e.g., resiliently deformed upon release ofdistracting forces and repositioning of the opposing bone surface.

[0036] For instance, a preformed composition is provided, formedinitially by the ex vivo onset of cure, in which the composition can beimplanted within on the order of 10 seconds to several days of the onsetof cure, preferably within about 30 seconds to about 10 minutes, andmore preferably within about one to about five minutes, whilemaintaining a surface exotherm of less than about 50 C., and morepreferably less than about 45 C. once positioned within the body.

[0037] Once positioned in vivo, preferred preformed components of thisinvention are adapted to be finally shaped, for a period of betweenabout 10 seconds and one or more hours, and more preferably betweenabout one minute and about five minutes. The lower limit is definedlargely by the time it takes to effectively reposition bone, orotherwise re-establish suitable force on the implant. The upper limit,in turn, is generally defined by the susceptibility of the implantedcomposition to further deformation or shaping. Such final shaping isgenerally accomplished, at least in part, under the force brought aboutby repositioning articulating bone surfaces. In one preferredembodiment, the partially cured composition is implanted underconditions that permit it to deform less than about 15%, preferably lessthan about 10%, and most preferably less than about 5%, underphysiologic forces, while maintaining tibial congruency and impartingdesired angular correction.

[0038] Hence, a particularly preferred preformed component of thisinvention can be implanted within an initial about one to about fiveminutes of the onset of its formation, and once implanted can be furthermolded or formed for a further period of about one to about fiveadditional minutes, in a manner that permits the resultant implant tosubstantially retain a desired final form and function.

[0039] The system of the present invention thereby provides the surgeonwith a variety of options, based on the manner in which these curing andforming processes are correlated. In one particularly preferredembodiment, for instance, the surgeon is provided with a compositionadapted to be partially cured and generally formed ex vivo, and thenpromptly inserted into the body and positioned at the joint site, whereit can be finally, and specifically, formed in the course of becomingfully cured.

[0040] By partially curing the prosthesis ex vivo, the present systemsimplifies the preparation process considerably, e.g., by lessening oravoiding potential problems (such as curing in the presence of moisture,and surface exotherm in the presence of tissue) that can arise when acomparable composition is mixed and delivered to the joint site while itis still flowable. Surprisingly, the present system permits suchprostheses to be not only formed, but also manipulated and inserted intothe joint (e.g., through an incision of between about 1 cm and about 3cm). Once inserted, the prosthesis can be positioned, and further formedin situ, all within a reasonable time frame. In fact, it has been foundthat the procedure is amenable to outpatient use and even regionalanesthesia.

[0041] Moreover, the present system can avoid the use of such processesas the drilling anchor holes into the underlying bone, distraction ofthe knee joint, ligament release, leveling of the tibial plateau, andthe various other procedures typically involved with delivering thebiomaterial directly to the joint site in still flowable form. Yet, theprosthesis of the present invention provides a combination of propertiessuch as the extent of congruence with underlying bone, wearcharacteristics, fracture toughness, and avoidance of fibrillatedarticular cartilage, that meets or exceeds the combination of propertiesobtained using a comparable biomaterial in flowable form, delivered andlargely cured in situ.

[0042] In addition to its immediate use in such joints as the knee, thesystem of the present invention provides particular advantages whenapplied to ball and socket joints, such as the hip. In one suchembodiment, a balloon can be filled with a biomaterial as describedherein, and inserted and positioned within the acetabulum, prior to orfollowing filling, to provide a soft, conformable, durable lining forthe placement of a hip prosthetic portion.

[0043] In a further embodiment, the method and system involve thepreparation and use of one or more partially or fully cured component(s)formed outside the body, for insertion and placement into the body andoptionally further fitting and securing at the joint site. Thesepreformed component(s) typically require less manipulation at thebedside and allow for alternative methods of terminal sterilization, andfinal inspection and release at the manufacturing site.

DETAILED DESCRIPTION

[0044] The method and system (e.g., preformed component(s) and/orcurable biomaterial and mold) can be used to prepare a final prosthesis,in vivo, that provides a first major surface in apposition to andretained upon the supporting bone itself, and a second (generallysubstantially parallel and opposite) major surface adapted to provide awear surface for opposing (e.g., articulating) bone. By “retained upon”it is meant that the final prosthesis is maintained in a desiredposition upon the supporting bone surface in a manner suitable for itsintended use, e.g., by the use of one or more anchor points, by the useof adhesive or other suitable interface materials, by the use ofsutures, staples, and the like, and/or by a mechanical lock achieved bythe combination of a bone-contacting surface suitably conformed orconformable to the terrain of supporting bone, together with theretaining (and optionally including deforming) effect achieved uponrepositioning opposing articulating bone surface.

[0045] The first and second major surfaces can be provided in anysuitable manner, for instance, 1) by the preparation and insertion of asingle partially cured and generally preformed component into the joint,preferably under conditions that permit the component to become further,and specifically, formed in vivo, 2) by adding a flowable biomaterial toan initial preformed component (e.g., in the shape of a balloon or openmold) positioned at the tissue site, 3) by placing one or more fullycured and preformed components at the tissue site and optionally furtherfitting, adapting and/or securing the component(s) as needed, and/or 4)by assembling one or more preformed components in situ (e.g., side byside in an interlocking fashion upon the surface) such that theassembled components cooperate to provide the first and second majorsurfaces.

[0046] In addition to the partially or fully cured preformedcomponent(s) and/or curable biomaterial and related molds, the methodand system of this invention include the optional use of variousadditional materials and/or steps, e.g., to prepare the bone surfaceitself, to provide suitable interfaces (e.g., adhesive interfaces and/orprotrusions that can be further secured to the joint site or bysmoothing of the femoral condyle or tibial plateau as needed), to treatone or more surfaces in order to provide them with different or improvedproperties as compared to the inherent properties of the materialproviding the surface, and the like. Examples of such materials include,for instance, the use of adhesive materials, tissue in-growthstimulators, and fibrous materials (e.g., webs adapted to tether theimplant and/or to facilitate fibrous tissue ingrowth).

[0047] The partially or fully cured preformed component(s) canthemselves each provide uniform or non-uniform properties, and can beprovided in a plurality or range of styles and sizes. These componentscan be designed to conform to lateral or medial compartments, or both,and to right or left knees, or both. In a preferred embodiment, allembodiments can be inserted into the joint site in a minimally invasivefashion. By “minimally invasive”, in this context, it is meant that theprocedure of sizing, inserting, positioning and forming the prosthesis,in situ, can preferably be accomplished without the need for open,invasive incisions of the type conventionally used for inserting totalknee prostheses. In a preferred embodiment, the partially curedpreformed components can be further formed and fully cured in vivo toenhance compliance with the joint site.

[0048] The surface of the partially or fully cured preformedcomponent(s) can also be modified to provide any desired properties(e.g., promote adhesion), such as by the design and use of polymersthemselves or by surface treatment of the fully cured or curingembodiments to provide suitable reactive groups such as amines, hydroxylgroups, or other reactive or hydrogen bonding functionalities.Similarly, the partially cured preformed component or fully curedcomponent, including balloons or composite materials, can be providedwith appropriate surface coatings, e.g., biologically active agents topromote desired tissue interactions, including tissue or cellularadhesion, such as those selected from the group consisting of cytokines,hydroxyapatite, collagen, and combinations thereof.

[0049] In one embodiment of this invention, partially cured, andgenerally preformed components are inserted into the joint site, andthere further and specifically formed to enhance compliance. In analternative embodiment, fully cured components in the shape of a balloonor open mold are employed to provide a final composite material byinserting the balloon or mold into the joint and there filling it with abiomaterial that cures in situ and conforms with the joint site. Inanother alternative embodiment, the fully cured component(s) areprovided and inserted into the joint either singly or piecemeal andoptionally further fitted and secured in vivo.

[0050] As an example of the first such embodiment, the inventionprovides an open ex vivo mold, adapted to approximate the desireddimensions of the joint site, and to receive a curable biomaterial. Asuitable mold can be formed, for instance, from the use of conventionalmaterials such as silicone materials, that permit the curing biomaterialcomponent to be easily and entirely removed at the desired time.Optionally, the mold can itself be provided with a coating or releaseliner, including those that can be integrated, in whole or in part, withthe component thus formed. Once the flowable biomaterial has beendelivered and partially cured in this ex vivo mold, and any optionalmolding or fabricating steps have occurred, the biomaterial can beremoved from the mold and inserted into the joint site, under conditionssuitable to permit it to be further and finally formed in vivo toenhance conformance with the joint site. Optionally, additional ex vivoforming steps or features can be performed, e.g., by imparting desiredcurvature and femoral glide paths, prior to inserting and final formingin vivo.

[0051] Also, in the course of molding the component ex vivo, and/ortransferring it to the tissue site, various structures and/or materialscan be incorporated into and/or onto the component itself, to enhanceits placement, retention and/or performance in situ. For instance, themold itself can be provided in a form sufficient to impart variousintegral structural features, such as tibial “tabs”, adapted to provideor improve the retention of the component at the tissue site. Such tabs,for instance, can be provided in the form of one or more protrusionsintegral with the mold itself and adapted to be positioned within and/oraffixed to the soft tissue and/or bone in vivo. Examples of such tabsare shown, for instance, in FIG. 1, where reference number 18 depicts araised posterior portion.

[0052] An insertable component can also be provided with one or moreancillary portions or protrusions formed of materials other than thatused to form the bulk of the component itself. For instance, sutures orfibrous materials can be incorporated into or onto the bulk material,for use in improving the initial and/or long term retention of thecomponent in situ, e.g, by tethering the prosthesis at the joint siteand in a desired position. Such other materials can be temporarilypositioned into or upon the mold itself, for instance, or otherwiseprovided, in a manner that permits them to become integrated into thebiomaterial as it fills the mold and becomes partially cured ex vivo.With the resulting component positioned in situ, the protrusions can beused to tether the implant, by securing them to the surrounding softtissue and/or bone by use of adhesives, sutures, screws, pins, staplesor the like or combinations thereof. The materials can provide both animmediate fixation function, and optionally also a desired long termfunction, by permitting them to be either absorbed by the body overtime, and/or to permit or encourage fibrous tissue ingrowth for longterm fixation.

[0053] The reinforcing material can be provided in any suitable form,e.g., as fibers (e.g., sutures) or as a uniform woven or non-wovenfabric, optionally including one or more reinforcing fibers or layers. Asuitable non-woven fabric, for instance, is preferably a material suchas is commercially available under the trade name Trevira Spunbond fromHoechst Celanese Corporation. The non-woven fabric is generally composedof continuous thermoplastic fiber, needle punched together to yield afelt-like fabric. In addition to fabrics like Trevira Spunbond, othermaterials such as polyester staple mat, glass fiber mat, as well asother organic and inorganic fiber mats and fabrics can be employed.

[0054] Reinforcing fibers can be included within the woven or non-wovenfabric, or provided as separate layers of a composite. Such fiber layerscan preferably include a directional reinforcing fiber layer of organicor inorganic structural reinforcing fibers such as fiberglass, carbonfibers, aramid fibers which is available from DuPont Corporation underthe trade name Kevlar, linear polyethylene or polypropylene fibers suchas is commercially available from Allied-Signal, Inc. (now Honeywell)under the trade name Spectra, or polyester fibers. The phrase“reinforcing fiber” can include any fiber which, when used in its ownright or added to a composite fabric material, retains or enhancesdesired structural properties. The fibers can be randomly oriented, orpreferentially, they can be oriented in one or more directions. While anumber of specific types of materials have been given for use as thereinforcing fiber layer, it will be appreciated by those of ordinaryskill in the art that other equivalent-type reinforcing fiber layers canbe employed in the practice of the invention. A reinforcing fiber layercan be itself used to secure the prosthesis, or can be attached to awoven or non-woven fiber layer having a number of interstices or pores.Preferably, the reinforcing fiber layer and other fiber layers aresecured to each other mechanically, as by conventional stitching, needlepunching, stapling or buttons. In the case of certain applications,adhesives can also be used.

[0055] Similarly, a partially cured preformed component (and/orancillary portions incorporated therein) can also be provided withsuitable means to improve its ability to retain the component in situ,e.g., by the use of surface characteristics that provide improvedchemical interactions with the joint site. Such interactions can beachieved by the judicious use of bulk material compositions themselvesand/or the use of adhesives or other suitable interface materials. Thepartially cured, preformed, component can also be physically modified toincrease its interactions with joint site, as by surface roughening,etching or cross-hatching, which would tend to provide increased surfacearea, and in turn, improved mechanical retention. A partially cured,preformed, component can also be retained by external means that areotherwise secured to the surrounding bone and/or soft tissue by use ofadhesives, sutures, screws, pins, staples or the like or combinationsthereof. On the major surface opposing articulating bone, the partiallycured preformed component can be provided with suitable means as well,intended to improve or alter either its compliance and/or interactionswith the opposing bone surface.

[0056] In one particularly preferred embodiment, the system includes apartially cured preformed component that is first molded outside of thejoint site and adapted to be delivered to a tissue site and therepositioned in a fixed position. The mold can be of an open or closedconfiguration (and/or can involve a one- or multi-step molding process),adapted to preform one or both major surfaces, respectively. Oncepositioned, the partially cured component is adapted to be initially fitand positioned within the joint site, and to thereafter become betterconformed to the specific dimensions and/or terrain (e.g., anatomicstructure) of the joint site in vivo. Optionally, and preferably, themolds are designed to yield components that have optimum adhesion andconformance to the joint sites. The molds may also be heated during theex vivo partial curing process to optimize component properties or toprovide a component that is more formable in vivo.

[0057] In an alternative preferred embodiment, the method and systeminvolve the preparation and use of one or more fully or partially curedcomponent(s) formed outside the body, for insertion and placement intothe body and optionally further fitting and securing at the joint site.In one embodiment, the invention provides a single preformed componentthat is inserted into the joint site and optionally further fitted orsecured as needed. In another embodiment, the invention provides aplurality of preformed components, formed of the same or differentmaterials, and adapted to be delivered and positioned at the tissue sitein a manner that provides a final composite. The components can becombined at the site in any suitable fashion, e.g., by providing amechanical lock and/or by the use of interfacial materials such asadhesive layers. The components can be combined in any suitable fashion,e.g., as layers upon the bone, or as individual side-by-side componentsadapted to traverse the bone surface when combined. The use of preformedcomponent(s) can require less manipulation at the bedside and allow foralternative methods of terminal sterilization, and final inspection andrelease at the manufacturing site. The various means of retainingpartially cured preformed components, discussed herein, can be adaptedto work with fully cured preformed components.

[0058] The method and system of this invention can be used for repairinga variety of mammalian joints, including human joints selected from thegroup consisting of the tibial plateau of the knee, the acetabulum ofthe hip, the glenoid of the shoulder, the acromion process of theshoulder, the acromio-clavicular joint of the shoulder, the distaltibial surface of the ankle, the radial head of the elbow, the distalradius of the forearm, the proximal phalanx surface of the great toe,the proximal metacarpal surface of the thumb, and the trapezium of thewrist.

[0059] Those portions or combinations of preformed component(s) thatcontact the bone surface are preferably adapted to physically conformclosely to the prepared bone surface, e.g., to its macroscopic physicalcontours. Such conformation can be provided or enhanced in any suitablemanner, e.g., 1) by providing a partially cured preformed component thatis first made in an ex vivo mold and then adapted or modified to conformto the surface (e.g., by further forming in vivo), and/or 2) by use of apreformed balloon or composite mold material that is inserted into thejoint site and filled with a flowable biomaterial that cures in vivo sothat it conforms with the joint site and/or 3) by the use of fully curedpreformed component(s) that has optimum geometry for biomaterialcompliance once placed in the joint site and/or 4) by the preparationand use of a suitable (e.g., thin) interface material between bone andpreformed component (e.g., adhesive, filler, or cement material), and/or5) by the use of physical restraining means, such as adhesives, pins,staples screws, sutures or the like that are attached to protrusions inthe component itself or to an external means of securing it.

[0060] The method and system of this invention will be further describedwith reference to the Drawing, wherein

[0061]FIG. 1 shows a top and side perspective of a preferred preformedknee implant (10) prepared using an ex vivo mold according to thepresent invention. The implant provides a first major surface (12)adapted to be positioned upon the tibial surface, and a generally planarsecond major surface (14) adapted to be positioned against the femoralcondyle. In a typical embodiment, the second major surface, in turn, ispreferably provided with a femoral glide path (16) to facilitate itsperformance in situ, in the form of a generally central oval depressionabout 1 mm to about 5 mm deep at its lowest point (2 mm as shown) andabout 30 mm to about 50 mm in length by 10 mm to 30 mm in width (40 mmby 20 mm as shown). Those skilled in the art, given the presentdescription, will readily determine the actual dimensions for optimaluse, in both absolute and relative terms, depending on such factors asthe actual joint size and desired results (e.g., angular correction). Asshown, the implant is also provided with a raised tibial projection(18), adapted to catch the posterior portion of the tibial plateau. Theimplant can have dimensions on the order of between about 40 to about 60mm in the anterior-posterior dimension, between about 30 mm to about 40mm in the medial-lateral dimension, and a maximum thickness (at theposterior lip of between about 10 mm and about 20 mm.

[0062]FIG. 2 shows an embodiments in which a plurality of preformedcomponents are adapted to be inserted and assembled in situ to providethe final implant (20) FIG. 2a shows an embodiment, in which preformedcomponents (22 through 25, respectively) are assembled in a side-by-sidemanner sequentially, and in situ, and upon the tibial surface. Thematable preformed sections each provide at least a portion of theresultant bone-contacting surface and wear surface, as well as one ormore portions adapted to provide a mechanical lock with one or morerespective other portions. The mechanical lock can be achieved in anysuitable manner, as by the provision of corresponding male and femaleportions, respectively. The portions can be mated, in situ, e.g., in apress fit or sliding manner, in order to attach the respectivecomponents. As can be seen in the raised perspective of the sameembodiment, and FIG. 2b, in the resultant assembly, the combinedcomponents cooperate to provide both a tibial bone-contacting surface(28) and a wear surface (26).

[0063] In the alternative embodiment of FIG. 3, rather than beingpositioned in a side-by-side fashion across the bone surface (as in FIG.2), a final implant is provided using interlocking preformed components(show in this case as portions 31 through 33, respectively) are insteadprovided in a form that permits them to be stacked upon each other,e.g., by layering or sliding them onto each other, and positioned uponthe surface, in situ. The portions can be assembled in any suitablefashion, e.g., entirely on the tissue site, entirely ex vivo, or invarying combinations as desired. Optionally, and preferably, thegenerally planar portions are provided with corresponding matableportions, e.g., in the form of grooves and tabs to provide a slidingfit, or a depression and corresponding projection to provide either apress fit, snap fit, or other suitable fit sufficient to prevent lateraldisplacement to the extent desired. The resultant formed prostheticimplant can be provided with various features as described herein,including desired molded portions adapted to provide better fit orperformance. Top portion (31) is particularly well suited to provide adesirable wear surface, while one or more intermediate portions (asshown by element 32) are adapted to provide an optimal combination ofsuch properties as thickness, cushioning, and angular correction. Asshown the lowermost portion (33) is shown with a projection (34) adaptedto be retained within a corresponding anchor hole or suitable depressionformed into the bone itself. FIGS. 3b and 3 c provide generally bottomand top views, respectively, showing the manner in which the portionscan be combined in a layered fashion.

[0064] In the embodiment of FIG. 3, preformed layers are shown havingprotrusions adapted to be positioned in a corresponding indentationwithin each underlying layer (or bone), in order to form a compactstack. In such an embodiment, the corresponding system will typicallyinclude at least two preformed components, including the initial,bone-contacting component, and final component providing the wearsurface. The system can provide one or more intermediate layers, e.g.,the number and/or selection of which can be used to provide a finaldesired height to the overall composite, and/or to provide differingproperties (e.g., with respect to compressibility, resilience, tissueingrowth), and/or to provide improved retention between the first andfinal components.

[0065]FIG. 4a shows an embodiment in which a substantially open(saucer-shaped) mold (40) is inserted into the joint site, to be filledwith a corresponding curable biomateral in situ. The top (42) of themold is open to receive biomaterial (not show), while the bottom (44)provides a lower major surface (46) adapted to contact bone andterminates in a filled protrusion (48) adapted to be positioned within acorresponding anchor point drilled in the bone itself. The anterior edge(50) of the cup is substantially perpendicular to the plane of the cupitself, while the posterior edge (52) is tapered (and optionally raised)to accommodate the corresponding shape of the tibial spine.

[0066] As shown, and for use in an adult human, the ex vivo moldaccommodates a predetermined volume of biomaterial of on the order ofabout 5 ml to about 15 ml. As a further advantage of this invention, theamount of biomaterial actually can be predetermined and controlled tocorrespond with the ex vivo mold volume. In addition the ex vivo moldsare designed for optimum sizing and conformance to the joint site andMRI software may be used to chose best mold for joint site. Implantthickness and hence angular correction can be controlled in this way.

[0067]FIG. 4b shows a bottom perspective view of the mold apparatus ofFIG. 4a, showing the filled protrusion (48). The posterior edge portion(and particularly the posterior mesial edge portion, as seen in thefigure) can be seen as provided with a groove or indentation (54), againto accommodate the typical shape of the corresponding tibial spine.Overall, the mold can be seen as assuming a generally kidney-shapedconfiguration, adapted to correspond with the tibial surface. Such amold can be provided in a plurality of sizes, and shapes, to be selectedat the time of use to accommodate the particular patient's needs andsurgeon's desires.

[0068]FIGS. 5a and 5 b show the mold of FIG. 4a being positioned upon atibial surface (FIG. 5a), with the protrusion positioned within acorresponding anchor point, and (in FIG. 5b) with the tip of abiomaterial delivery cannula (56) positioned upon it, and with flowablebiomaterial (58) being shown in the course of delivery.

[0069]FIG. 6 shows a variety of alternative embodiments that include oneor more preformed component. FIG. 6a shows a simple wedge shapedembodiment (60), in which the posterior portion (62) is significantlyincreased in size as compared to the anterior (64). FIG. 6b shows animplant (66) molded to provide portions (here, layers) having differingwear characteristics, including a preformed top having improved wear ascompared to the separately formed bottom portion (70). FIG. 6c, bycomparison, shows a plurality of components (72) adapted to bepositioned and assembled in situ at the time of surgery. These includean upper portion (74) having improved wear characteristics as comparedto the others, a bottom portion (78) being suitably formed to thepatient's geometry and desired angular correction, and one (or more)central portions (76) adapted to be positioned between the top andbottom portions to achieve desired properties such as overall thickness,angles, and/or physical chemical properties (such as moduli).

[0070] The embodiment of FIG. 6d shows a single piece (80) as might becut from preformed material at the time of surgery, while FIG. 7 shows avariety of alternative means for anchoring a preformed component such asthat shown in FIG. 6d. These include the use of a grout (82) or othersuitable interface material as shown in FIG. 7a; the use of a separateexternal retaining device (84) as shown in FIG. 7b; the use ofexternally provided pins, screws, sutures, etc. as exemplified byelements (86) which generally traverse the body itself as in FIG. 7c;and the use of one or more anchor portions (88) positioned along one ormore suitable surfaces as shown in FIG. 7d.

[0071]FIG. 8 shows a further variety for anchoring or stabilizing apreformed portion by the use of ancillary portions and/or surfacetexture, including a roughened surface (90) as in FIG. 8a; or tabs(e.g., provided by fabric or suture like materials) as shown as elements92 and 94 of FIGS. 8b and 8 c, respectively. In practice, the preformedcomponents can benefit from any suitable combination of the variousfeatures and embodiments described or shown herein.

[0072]FIG. 9 shows a variety of embodiments in a substantially closed(balloon like) mold is adapted to be inserted into the joint site andfilled with a corresponding curable biomaterial, the mold itselfproviding a preformed articulating wear surface, including FIG. 9a whichshows an inflatable balloon portion (96) that includes an integralpreformed wear surface and portion (98), as well as a lumen (100)adapted to fill the inflatable portion with flowable biomaterial. FIG.9b shows a corresponding balloon (102) though without a preformedportion, and including its biomaterial lumen (104). Although not shown,the balloon of this or any embodiment can include various interiorand/or exterior surface coatings, and can have regions and/or layershaving different desired physical-chemical properties (such asporosity). FIG. 9c shows a bi-compartmental closed balloon-like mold(106), wherein each compartment is adapted to conform to a respectivemedial or lateral tibial surface.

[0073]FIG. 10 shows a mold adapted for use as an acetabular mold (110)in connection with the replacement of the articulating surface in a hip,when filled with biomaterial, the mold forming a concave portion adaptedto retain a corresponding femoral head. The mold is shown providing athin generally cup-shaped mold adapted to be filled in any suitable form(e.g., using a removable conduit (not shown) attached to the spacebetween inner and outer sealed layers (116 and 114, respectively)forming the mold.

[0074]FIG. 11 shows a patella-femoral joint form suitable for use incombination with the method and system of this invention. As shown inthe views of 11 a through 11 c, the form includes a silicone or othersuitable pad material (122) having aluminum or other suitable stayportions (124) and terminal handle or grasping portions (126). In use,with the knee at a generally 45 degree angle, the piece is formed to thefemoral bone surface, with its form maintained by bending the aluminumstays. With anchor points cut into the femoral bone, if desired, theform is held tight against the bone with the upper handle held away frombone to permit the delivery of curable biopolymer between the form andthe bone. As polymer is placed onto the bone (and into any anchorpoints) the form is maintained for a time sufficient to suitably formthe polymer, whereafter it can be removed.

[0075] As described in Applicant's co-pending U.S. provisionalapplication 60/228,444, the present application describes a method andsystem for the creation or modification of the wear surface using animplanted material fixed to the support structure of the original wearsurface, to generally conform to the shape of the original surface in amammal. A method or system where the end of the bony surface is arotating, sliding or rolling surface, such as in the knee, finger, hip,toe, spine, wrist, elbow, shoulder, ankle, or TMJ joint. The implantwill function:

[0076] a) as a spacer,

[0077] b) as an impact absorber

[0078] c) as a surface with improved coefficient of friction (ascompared to the diseased surface), and/or

[0079] d) to increase the weight bearing area and improve congruency ofthe joint surface (as compared to the diseased condition).

[0080] The method and system of this invention can be applied to areasof aseptic necrosis, such as the nevecular bone in the wrist. Thematerial to be implanted consists of a plurality of materials, such aspolymers, including polyurethane, polyethyelenes, polyureas,polyacrylates, polyurethane acrylates, hydrogels, epoxies and/or hybridsof any of the above.

[0081] In an alternative embodiment, the surface can be provided by anyof a series of metals, including titanium, stainless steel, cobaltchrome millithium alloys and tantalum. Other surface materials caninclude various ceramics and biologic polymers.

[0082] The implantable material for the resurfacing can be formed exvivo and/or in vivo as an injectable material that sets up to the moldedshape. The methods for changing state from liquid to solid state includecooling or heating, the passage of time, which allows for a change ofstate, or a chemical reaction between different reactants. The reactioncan be exothermic or endothermic. The set-up can be light activated orchemically catalyzed or it could be heat activated. Examples of suchsystems include flowable polymers of two or more components, lightactivated polymers, and polymers cured either by catalysts or by heat,including body heat. Molds can be used in the form of balloons, dams orretainers. They can be used in combination with the local anatomy toproduce the desired shape and geometry. Molds can be of materials thatare retained and becomes part of the implant or could be removed aftercuring of the biomaterial component.

[0083] In an alternative embodiment, the material would be semi-solidand could be shaped and then set up in vivo. This would allow for theminimally invasive application, either through an arthroscopic portal orthrough a small mini arthrotomy. As a further embodiment, the materialcould be synthesized ex vivo and then machined to fit using imaging topre-determine the desired geometry and size of the implant. As a furtheralternative, a range of implant sizes could be provided and sizing couldbe accomplished during the procedure. An ex vivo mold could be fit usingmolding materials and the implant could be molded on site just prior toimplantation.

[0084] Fixation methods for the implant would include biologic glues toglue the implant to the underlying surface, trapping of the implant intoa cavity on the surface that causes a mechanical lock, using variousanchors to the underlying structure and fixing the implant to thatsurface or using mold retainers and/or screws, staples, sutures or pins.In alternative embodiment, anchors in the underlying structure may beused for fixing the implant to that surface and we may also use a tissueingrowth system to secure anchoring.

[0085] In the preferred embodiment, the patient will have a diagnosis ofosteoarthritis and have loss of cartilage on the articulating surface. Adetermination will be made of the amount of correction needed for thereestablishment of a normal angle of articulation. The ligaments will bebalanced so that there is no loss of range of motion with the implant inplace and the surface will be placed in such a position that theeventual resulting surface geometry reestablishes the same plane andorientation of the original articular surface.

[0086] Access to the site is obtained in a minimally invasive way. In apreferred embodiment, this is accomplished through arthroscopic meanswith arthroscopic portals. In an alternative embodiment, the access isaccomplished by a mini arthrotomy with a small incision that allowsaccess to the joint without sacrificing nerves, vessels, muscles orligaments surrounding the joint. In the preferred embodiment fibrillatedarticulating cartilage that is degenerated is removed down to thesubchondral surface. The surface is dried and prepared for appropriateanchoring. This may include anchor points that give a mechanical lock orthat alternatively simply supply horizontal and lateral stability. Thesurface may be prepared by drying and roughening in case a tissueadhesive is used. Pre-made anchors may be installed. These may be madeof various metallic materials or of polymers and may consist of pegsthat would extend up through the implant to anchor it to the underlyingsurface. This surrounding subchondral bone may be roughened to enhancetissue ingrowth or implant adhesion. The final geometry of the implantmay be determined by a dam or mold that is placed on the joint at thetime the material is implanted, when the implant is installed using anin situ cured technique (in the manner shown in FIGS. 1 and 4 ofApplicant's provisional parent application).

[0087] For pre-made material formed at the surgical site within a mold,various forms of stabilization could be used, including anchor points ortitanium screws. Alternatively, the pre-made material could be made offsite to the specs developed from imaging of the patient's joint surface.In a third embodiment, multiple sizes could be made off site and theselection of the appropriate implant size could be chosen at the time ofsurgery. Two alternatives shown in FIG. 2 of the parent provisionalapplication include a single segment that can be installed through aportal or a series of segments that can be installed through a portaland locked together once inside the joint. They would be placedsequentially and then anchored to the bone by anchor points cut in thebone or by screws or tissue ingrowth. Finally, a robot, a jag or othercutting fixture could be used to prepare the bony surface for thepre-made implant to a fixed geometry of the anchor point.

[0088] Both the preformed component(s) and flowable biomaterial, ifused, can be prepared from any suitable material. Typically, thematerials include polymeric materials, having an optimal combination ofsuch properties as biocompatibility, physical strength and durability,and compatibility with other components (and/or biomaterials) used inthe assembly of a final composite. Examples of suitable materials foruse in preparing the preformed component(s) may be the same or differentfrom the in situ curing biomaterial, and include polyurethanes,polyethylenes, polypropylenes, Dacrons, polyureas, hydrogels, metals,ceramics, epoxies, polysiloxanes, polyacrylates, as well as biopolymers,such as collagen or collagen-based materials or the like andcombinations thereof.

[0089] Examples of suitable materials for use in preparing the flowablebiomaterial, if used, include polyurethanes, polyureas, hydrogels,epoxies, polysiloxanes, polyacrylates, and combinations thereof.

[0090] In a presently preferred embodiment, the preformed component(s)and the flowable biomaterial, if included, each comprise a biocompatiblepolyurethane. The same or different polyurethane formulations can beused to form both the preformed component(s), e.g., by an injectionmolding technique, as well as for the flowable biomaterial, if present.

[0091] Suitable polyurethanes for use as either the preformed componentor biomaterial can be prepared by combining: (1) a quasi-prepolymercomponent comprising the reaction product of one or more polyols, andone or more diisocyanates, and optionally, one or more hydrophobicadditives, and (2) a curative component comprising one or more polyols,one or more chain extenders, one or more catalysts, and optionally,other ingredients such as an antioxidant, and hydrophobic additive.

[0092] In the embodiment in which an in situ curing polymer is used, thepresent invention preferably provides a biomaterial in the form of acurable polyurethane composition comprising a plurality of parts capableof being mixed at the time of use in order to provide a flowablecomposition and initiate cure, the parts including: (1) aquasi-prepolymer component comprising the reaction product of one ormore polyols, and one or more diisocyanates, optionally, one or morehydrophobic additives, and (2) a curative component comprising one ormore polyols, one or more chain extenders, one or more catalysts, andoptionally, other ingredients such as an antioxidant, hydrophobicadditive and dye. Upon mixing, the composition is sufficiently flowableto permit it to be delivered to the body, and there be fully cured underphysiological conditions. Preferably, the component parts are themselvesflowable, or can be rendered flowable, in order to facilitate theirmixing and use.

[0093] The flowable biomaterial used in this invention preferablyincludes polyurethane prepolymer components that react either ex vivo orin situ to form solid polyurethane (“PU”). The formed PU, in turn,includes both hard and soft segments. The hard segments are typicallycomprised of stiffer oligourethane units formed from diisocyanate andchain extender, while the soft segments are typically comprised of oneor more flexible polyol units. These two types of segments willgenerally phase separate to form hard and soft segment domains, sincethey tend to be incompatible with one another. Those skilled in therelevant art, given the present teaching, will appreciate the manner inwhich the relative amounts of the hard and soft segments in the formedpolyurethane, as well as the degree of phase segregation, can have asignificant impact on the final physical and mechanical properties ofthe polymer. Those skilled in the art will, in turn, appreciate themanner in which such polymer compositions can be manipulated to producecured and curing polymers with desired combination of properties withinthe scope of this invention.

[0094] The hard segments of the polymer can be formed by a reactionbetween the diisocyanate or multifunctional isocyanate and chainextender. Some examples of suitable isocyanates for preparation of thehard segment of this invention include aromatic diisocyanates and theirpolymeric form or mixtures of isomers or combinations thereof, such astoluene diisocyanates, naphthalene diisocyanates, phenylenediisocyanates, xylylene diisocyanates, and diphenylmethanediisocyanates, and other aromatic polyisocyanates known in the art.Other examples of suitable polyisocyanates for preparation of the hardsegment of this invention include aliphatic and cycloaliphaticisocyanates and their polymers or mixtures or combinations thereof, suchas cyclohexane diisocyanates, cyclohexyl-bis methylene diisocyanates,isophorone diisocyanates and hexamethylene diisocyanates and otheraliphatic polyisocyanates. Combinations of aromatic and aliphatic orarylakyl diisocyanates can also be used.

[0095] The isocyanate component can be provided in any suitable form,examples of which include 2,4′-diphenylmethane diisocyanate,4,4′-diphenylmethane diisocyanate, and mixtures or combinations of theseisomers, optionally together with small quantities of2,2′-diphenylmethane diisocyanate (typical of commercially availablediphenylmethane diisocyanates). Other examples include aromaticpolyisocyanates and their mixtures or combinations, such as are derivedfrom phosgenation of the condensation product of aniline andformaldehyde. It is suitable to use an isocyanate that has lowvolatility, such as diphenylmethane diisocyanate, rather than morevolatile materials such as toluene diisocyanate. An example of aparticularly suitable isocyanate component is the 4,4′-diphenylmethanediisocyanate (“MDI”). Alternatively, it can be provided in liquid formas a combination of 2,2′-, 2,4′- and 4,4′-isomers of MDI. In a preferredembodiment, the isocyanate is MDI and even more preferably4,4′-diphenylmethane diisocyanate.

[0096] Some examples of chain extenders for preparation of the hardsegment of this invention include, but are not limited, to short chaindiols or triols and their mixtures or combinations thereof, such as1,4-butane diol, 2-methyl-1,3-propane diol, 1,3-propane-diol ethyleneglycol, diethylene glycol, glycerol, cyclohexane dimethanol, triethanolamine, and methyldiethanol amine. Other examples of chain extenders forpreparation of the hard segment of this invention include, but are notlimited to, short chain diamines and their mixtures or combinationsthereof, such as dianiline, toluene diamine, cyclohexyl diamine, andother short chain diamines known in the art.

[0097] The soft segment consists of urethane terminated polyol moieties,which are formed by a reaction between the polyisocyanate ordiisocyanate or polymeric diisocyanate and polyol. Examples of suitablediisocyanates are denoted above. Some examples of polyols forpreparation of the soft segment of this invention include but are notlimited to polyalkylene oxide ethers derived form the condensation ofalkylene oxides (e.g. ethylene oxide, propylene oxide, and blendsthereof), as well as tetrahyrofuran based polytetramethylene etherglycols, polycaprolactone diols, polycarbonate diols and polyester diolsand combinations thereof. In a preferred embodiment, the polyols arepolytetrahydrofuran polyols (“PTHF”), also known as polytetramethyleneoxide (“PTMO”) or polytetramethylene ether glycols (“PTMEG”). Even morepreferably, the use of two or more of PTMO diols with differentmolecular weights selected from the commercially available groupconsisting of 250, 650,1000, 1400, 1800, 2000 and 2900.

[0098] Two or more PTMO diols of different molecular weight can be usedas a blend or separately, and in an independent fashion as between thedifferent parts of the two part system. The solidificationtemperature(s) of PTMO diols is generally proportional to theirmolecular weights. The compatibility of the PTMO diols with such chainextenders as 1,4-butanediol is generally in the reverse proportion tomolecular weight of the diol(s). Therefore the incorporation of the lowmolecular weight PTMO diols in the “curative” (part B) component, andhigher molecular weight PTMO diols in the prepolymer (part A) component,can provide a two-part system that can be used at relatively lowtemperature. In turn, good compatibility of the low molecular weightPTMO diols with such chain extenders as 1,4-butanediol permits thepreparation of two part systems with higher (prepolymer to curative)volume ratio. Amine terminated polyethers and/or polycarbonate-baseddiols can also be used for building of the soft segment.

[0099] The PU can be chemically crosslinked, e.g., by the addition ofmultifunctional or branched OH-terminated crosslinking agents or chainextenders, or multifunctional isocyanates. Some examples of suitablecrosslinking agents include, but are not limited to, trimethylol propane(“TMP”), glycerol, hydroxyl terminated polybutadienes, hydroxylterminated polybutadienes (HOPB), trimer alcohols, Castor oilpolyethyleneoxide (PEO), polypropyleneoxide (PPO) and PEO-PPO triols. Ina preferred embodiment, HOPB is used as the crosslinking agent.

[0100] This chemical crosslinking augments the physical or “virtual”crosslinking of the polymer by hard segment domains that are in theglassy state at the temperature of the application. The optimal level ofchemical cross-linking improves the compression set of the material,reduces the amount of the extractable components, and improves thebiodurability of the PU. This can be particularly useful in relativelysoft polyurethanes, such as those suitable for the repair of damagedcartilage. Reinforcement by virtual cross-links alone may not generatesufficient strength for in vivo performance in certain applications.Additional cross-linking from the soft segment, potentially generated bythe use of higher functional polyols can be used to provide stiffer andless elastomeric materials. In this manner a balancing of hard and softsegments, and their relative contributions to overall properties can beachieved.

[0101] Additionally, a polymer system of the present inventionpreferably contains at least one or more, biocompatible catalysts thatcan assist in controlling the curing process, including the followingperiods: (1) the induction period, and (2) the curing period of thebiomaterial. Together these two periods, including their absolute andrelative lengths, and the rate of acceleration or cure within eachperiod, determines the cure kinetics or profile for the composition.Some examples of suitable catalysts for preparation of the formed PU ofthis invention include, but are not limited to, tin and tertiary aminecompounds or combinations thereof such as dibutyl tin dilaurate, and tinor mixed tin catalysts including those available under the tradenames“Cotin 222”, “Formrez UL-22” (Witco), “dabco” (a triethylene diaminefrom Sigma-Aldrich), stannous octanoate, trimethyl amine, and triethylamine. In a preferred embodiment, the catalyst is Formrez UL-22 (Witco).In an alternative preferred embodiment, the catalyst is a combinationCotin 222 (CasChem) and dabco (Sigma-Aldrich).

[0102] The in vivo and ex vivo cured polyurethanes of this invention canbe formed by the reaction of two parts. Part I of which (alternativelyreferred to as Part A) includes a di- or multifunctional isocyanate orquasi-prepolymer which is the reaction product of one or moreOH-terminated components, and one or more isocyanates. Part II of thepolyurethane (alternatively referred to as Part B herein) is a curativecomponent that includes of one or more chain extenders and one or morepolyols, and one or more catalysts, and other additives such asantioxidants and dyes. For a suitable formed PU, the stoichiometrybetween Parts I (quasi-prepolymer) and II (curative component),expressed in terms of NCO:OH molar ratio of the isocyanate terminatedpre-polymer (Part I) and the curative component (Part II) is preferablywithin the range of about 0.8 to 1.0 to 1.2 to 1.0, and more preferablyfrom about 0.9 to 1 to about 1.1 to 1.0.

[0103] Optionally, a reactive polymer additive can be included and isselected from the group consisting of hydroxyl- or amine-terminatedcompounds selected from the group consisting of poybutadiene,polyisoprene, polyisobutylene, silicones, polyethylene-propylenediene,copolymers of butadiene with acryolnitrile, copolymers of butadiene withstyrene, copolymers of isoprene with acrylonitrile, copolymers ofisoprene with styrene, and mixtures of the above.

[0104] Suitable compositions for use in the present invention are thosepolymeric materials that provide an optimal combination of propertiesrelating to their manufacture, application, and in vivo use. In theuncured state, such properties include component miscibility orcompatibility, processability, and the ability to be adequatelysterilized or aseptically processed and stored. In the course ofapplying such compositions, suitable materials exhibit an optimalcombination of such properties as flowability, moldability, and in vivocurability. In the cured state, suitable compositions exhibit an optimalcombination of such properties as strength (e.g., tensile andcompressive), modulus, biocompatibility and biostability.

[0105] When cured, the compositions demonstrate an optimal combinationof properties, particularly in terms of their conformational stabilityand retention of physical shape, dissolution stability,biocompatibility, and physical performance, as well mechanicalproperties such as load-bearing strength, tensile strength, shearstrength, shear fatigue resistance, impact absorption, wear resistance,and surface abrasion resistance. Such performance can be evaluated usingprocedures commonly accepted for the evaluation of natural tissue andjoints, as well as the evaluation of materials and polymers in general.In particular, a preferred composition, in its cured form, exhibitsmechanical properties that approximate or exceed those of the naturaltissue it is intended to provide or replace.

[0106] To achieve these desirable uncured and delivery properties, a“polymer system”, as used herein refers to the component or componentsused to prepare a polymeric composition of the present invention. In apreferred embodiment, a polymer system comprises the componentsnecessary to form two parts: Part I being an NCO terminated pre-polymer(optionally referred to as an “isocyanate quasi-polymer”). Thequasi-polymer of Part I typically includes a polyol component,optionally in combination with a hydrophobic additive component, and anexcess of an isocyanate component. Part II of the two component systemcan include one long-chain polyols, chain extenders and/orcross-linkers, together with other ingredients (e.g., catalysts,stabilizers, plasticizers, antioxidants, dyes and the like). Suchadjuvants or ingredients can be added to or combined with any othercomponent thereof either prior to or at the time of mixing, delivery,and/or curing.

[0107] In a particularly preferred embodiment, a polymer system of thisinvention is provided as a plurality of component parts and employs oneor more catalysts. The component parts, including catalyst, can be mixedto initiate cure, and then delivered, set and fully cured underconditions (e.g., time and exotherm) sufficient for its desired purpose.Upon the completion of cure, the resultant composition provides anoptimal combination of properties for use in repairing or replacinginjured or damaged tissue. In a particularly preferred embodiment, theformulation provides an optimal combination of such properties ascompatibility and stability of the biomaterial parts, ex vivo or in situcure capability and characteristics (e.g., extractable levels,biocompatibility, thermal/mechanical properties), mechanical properties(e.g., tensile, tear and fatigue properties), and biostability.

[0108] The volume ratio of the parts can also be used to improve andaffect the uncured and curing properties Compositions having two or moreparts, are preferred. Where two parts are used, the relative volumes canrange, for instance, from 1:10 to 10:1 (quasi-prepolymer to curativecomponents, based on volume). A presently preferred range is between 2:1and 1:2. As those skilled in the art will appreciate, given the presentdescription, the optimal volume ratio is largely determined by thecompatibility and the stability of part A and B.

[0109] In choosing an optimal volume ratio for a given formulation,those skilled in the art, given the present description, will appreciatethe manner in which the following considerations can be addressed. Theviscosity of the reactive parts, at the temperature used for eitherinjection-molding preformed components, or for in situ cure, shouldprovide an acceptable degree of mixing and flow rate, without causingmechanical failure of any component of the delivery system includingcartridge, static mixer, gun and other components.

[0110] Preferably, the biomaterial is sufficiently flowable to permit itto be delivered (e.g., injected) into the mold or tissue site. Thecomposition of both reactive parts must be such that these parts arehomogeneous and phase stable in the temperature range of theapplication. Generally, the maximum temperature of the reaction exothermis proportional to the concentration of the reactive groups in the mixedpolymer. A high concentration of the reactive groups might evolve toohigh reaction exothermal energy and therefore cause thermal damage tothe surrounding tissues. The reactive parts will preferably remainsubstantially liquid in form during mixing.

[0111] A desired and stable volume ratio of the components can beachieved in any suitable manner, e.g., by the use of dual-compartmentcartridges with constant volume ratio or by using the injectors withdelivery rates independently variable for each component.

[0112] Compatibility of the composition can also be affected (andimproved) in other ways as well, e.g., by pre-heating the componentsprior to polymer application. To enhance the homogeneity of thecomponents, the components of a preferred composition of this inventionare preferably preheated before mixing and delivery, e.g., by heating toabout 60 C. to about 80 C. for about 2 to about 6 hours prior to use.Preferably, the composition parts are cooled back to about 35 C. to 37C. before use in injection.

[0113] Fully cured polymeric (e.g., polyurethane) biomaterials suitablefor use in forming components of this invention provide an optimalcombination of such properties as creep and abrasion resistance.Preferably, for instance, the biomaterial provides DIN abrasion valuesof less than about 100 mm³, more preferably less than about 80 mm³ andmost preferably less than about 60 mm³, as determined by ASTM TestMethod D5963-96 (“Standard Test Method for Rubber Property AbrasionResistance Rotary Drum Abrader”).

What is claimed is:
 1. A system for the creation or modification of thewear surface of an orthopedic joint within a mammalian body, the systemcomprising one or more partially or fully preformed polymericcomponents, adapted to be inserted and positioned at a joint site toprovide an implant having at least one major surface in apposition tosupporting bone, and at least a second major surface in apposition toopposing bone.
 2. A system according to claim 1 wherein one or more ofthe polymeric components are formed at the time of use, by the use of acurable polymer system adapted to be at least partially cured andpartially formed by ex vivo molding in order to provide an implantablecomponent adapted to be inserted and positioned in vivo, underconditions suitable to permit the implanted component to become finallyformed upon reestablishing the natural joint space and in conformancewith the opposing bone surfaces of the orthopedic joint site.
 3. Asystem according to claim 1 wherein the polymeric components comprise aplurality of packaged, preformed components adapted to be assembled atthe orthopedic joint site in a minimally invasive fashion to provide afinal prosthesis having surfaces in conformance with the opposing bonesurfaces of the orthopedic joint site.
 4. A system according to claim 1further comprising an ex vivo mold having a molding surface adapted toprovide a roughened, patterned, and/or contoured surface to thepartially preformed component, in a manner sufficient to provideimproved retention and fit of the component at the joint site.
 5. Asystem according to claim 4 wherein the mold further provides ancillarymeans adapted to be incorporated into the preformed component forsecuring the component once formed in the joint site.
 6. A systemaccording to claim 5 wherein the ancillary means comprise one or moreprotrusions adapted to be attached to either soft tissue and/or bone atthe joint site to improve fixation.
 7. A system according to claim 4wherein the contoured surface comprises a contour having one or moreprotrusions, integral with the preformed component, and formed duringthe ex vivo molding process.
 8. A system according to claim 6 whereinthe protrusions are adapted to be integrated into the preformedcomponent during the ex vivo molding process.
 9. A system according toclaim 7 wherein the protrusions are comprised of sutures and/or fibrousbiomaterials integrally formed with the component itself.
 10. A systemaccording to claim 4 further comprising separate means, not associatedwith the mold itself, for securing the component to the joint site,selected from the group consisting of adhesives, sutures, pins, staples,screws, and combinations thereof.
 11. A system according to claim 1wherein the one or more preformed polymeric component(s) are adapted tobe inserted into a joint in a minimally invasive fashion.
 12. A systemaccording to claim 2 in which the preformed component(s) and/orcorresponding mold(s) are provided in a plurality or range of styles andsizes for selection and use in the surgical field.
 13. A systemaccording to claim 1 wherein the implant is adapted for use on thetibial surface of the knee, and provides portions adapted to conform tothe shape of the femoral condyle and corresponding medial tibialplateau, lateral tibial plateau, or both.
 14. A system according toclaim 1 wherein the polymeric component is fabricated from a materialselected from the group consisting of polyurethanes, polyureas,hydrogels, polysiloxanes, polyacrylates, and epoxies, and combinationsthereof.
 15. A system according to claim 14 wherein the polymericcomponent comprises a polyurethane.
 16. A system according to claim 15wherein the polyurethane is prepared from polyisocyanate(s), short andlong chain polyols, and optionally including one or more ingredientsselected from the group hydrophobic additive(s), tin and/or aminecatalyst(s), and antioxidant(s).
 17. A system according to claim 16wherein the polyurethane comprises aromatic polyisocyanates, PTMO's, andshort chain diols.
 18. A system according to claim 16 wherein thehydrophobic additive comprises hydroxyl-terminated polybutadiene, andthe tin and/or amine catalyst(s) are adapted to promote theisocyanate-hydroxyl reaction preferentially and are selected from thegroup consisting of UL22, Cotin 222, 1,4-diazabicyclo[2.2.2]octane(dabco), and dibutyltin dilaurate (DBTDL), and combinations thereof. 19.A system according to claim 14, wherein the preformed polymericcomponent comprises one or more surfaces having attached thereto abiologically active agent selected from the group cytokines, growthfactors, autologous growth factors, hydroxyapatite, collagen, andcombinations thereof.
 20. A system according to claim 14 wherein thesurface of the preformed component is provided or modified with reactivegroups to promote tissue adhesion.
 21. A system according to claim 20wherein the reactive groups are provided by the polymers used tofabricate the polymeric component, and are selected from amines,hydroxyl groups, or other reactive or hydrogen bonding functionalities.22. A system for the creation or modification of the wear surface of anorthopedic joint within a mammalian body, the system comprising one ormore preformed polymeric components adapted to be positioned within thejoint site and one or more flowable biomaterial polymer compositionsadapted to be arthroscopically injected into contact with a preformedcomponent and cured in situ at the joint site in order to provide acomposite implant.
 23. A system according to claim 22 wherein thepreformed polymeric components comprise an inflatable balloon having apreformed top weight-bearing wear portion and a preformed bottom portionadapted to conform to the shape of supporting bone.
 24. A systemaccording to claim 23 wherein the one or more portions of the balloonare fabricated from a natural or synthetic fabric adapted to permittissue in-growth, and sufficiently permeable to permit air to escapewhile retaining the curable biomaterial.
 25. A system according to claim24 wherein the fabric is of sufficient permeability to permit physicalinterpenetration of the flowable polymer.
 26. A system according toclaim 23 wherein the bottom and/or top portions comprise materialsselected from polyurethanes, polyethylenes, polypropylenes, metals,ceramics, biopolymers or the like and combinations thereof.
 27. A systemaccording to claim 23 wherein the top and bottom portions are providedwith forms corresponding to the shape of a femoral condyle and tibialplateau, respectively.
 28. A system according to claim 23 wherein theballoon further comprises a port adapted to fill the balloon withflowable biomaterial in situ, in a manner sufficient to force the topportion toward corresponding bone.
 29. A system according to claim 23wherein the bottom portion provides a raised protrusion sufficient toimprove retention within the joint site and/or to provide a site forsuturing, stapling, pinning, or screwing the portion within the jointsite.
 30. A system according to claim 22 wherein separate means areprovided for securing the preformed component within the joint site. 31.A system according to claim 22, further comprising one or morebiologically active agents adapted to be provided on one or moresurfaces of the resultant composite implant.
 32. A system according toclaim 22 wherein the surface of the preformed component and/or resultantcomposite material are provided or modified with reactive groups topromote adhesion.
 33. A system according to claim 32 wherein thereactive groups are either provided by the preformed component itself,or are separately added by suitable surface treatment of the componentor resultant composite, and the reactive groups are selected fromamines, hydroxyl groups, or other reactive or hydrogen bondingfunctionalities.
 34. A system according to claim 22 in which one or moreof the preformed components are provided in a plurality or range ofstyles and sizes.
 35. A system according to claim 22 wherein the one ormore flowable biomaterial(s) are adapted to be inserted into a jointusing minimally invasive means.
 36. A system for the creation ormodification of the wear surface of an orthopedic joint within amammalian body, the system comprising a plurality of packaged, preformedcomponents adapted to be assembled at the orthopedic joint site in aminimally invasive fashion to provide a final prosthesis having surfacesin apposition to and conformance with the opposing bone surfaces of theorthopedic joint site.
 37. A system according to claim 36 wherein one ormore of the preformed components are provided with surfaces suitablyroughened, patterned, or contoured to provide maximum adhesion and fitwhen placed, and optionally further fitted and secured, within the jointsite.
 38. A system according to claim 36, wherein one or more of thepreformed components are formed at the time of use by the use of acurable bomaterial adapted to completely cure when preformed and thenplaced and optionally further fitted or secured inside the joint site.39. A system according to claim 36 wherein one or more of the preformedcomponents provide means for further securing the component once placedin the joint site.
 40. A system according to claim 39 wherein theretention means to secure the component includes the use of tissueadhesives to improve fixation.
 41. A system according to claim 39wherein the retention means comprise one or more protrusions adapted tobe sutured, pinned, stapled, screwed or combinations thereof orotherwise mechanically attached into the surrounding soft tissue and/orbone to improve fixation.
 42. A system according to claim 41 wherein theprotrusions are themselves integral with the preformed component.
 43. Asystem according to claim 42 wherein the protrusions are integrated intoa flowable biomaterial during the ex vivo molding process used to formthe preformed component.
 44. A system according to claim 43 wherein theprotrusions are comprised of sutures or fibrous materials.
 45. A systemaccording to claim 39 wherein means to secure the component are externalto it and secured once inside the joint site by the use of adhesives,sutures, pins, staples, screws or the like and combinations thereof toimprove fixation to the surrounding soft tissue and/or bone to improvefixation.
 46. A system according to claim 36 wherein the one or morepreformed component(s) are adapted to be inserted into a joint in aminimally invasive fashion.
 47. A system according to claim 36 in whichthe one or more preformed component(s) are provided in a plurality orrange of styles and sizes.
 48. A system according to claim 37 whereinthe assembled components conform to the shape of the femoral condyle andtibial plateau, medial, lateral or both.
 49. A system according to claim37 wherein the preformed component(s) are fabricated from materialsselected from the group consisting of polyurethanes, polyethylenes,polyureas, hydrogels, polysiloxanes, polyacrylates, epoxies, andcombinations thereof.
 50. A system according to claim 49 wherein thematerial comprises a polyurethane.
 51. A system according to claim 50wherein polyurethane is prepared from polyisocyanate(s), short and longchain polyols, and optionally including one or more ingredients selectedfrom the group hydrophobic additive(s), tin and/or amine catalyst(s),and antioxidant(s).
 52. A system according to claim 51 wherein thepolyurethanes are prepared from aromatic polyisocyanates, PTMO's, shortchain diols.
 53. A system according to claim 52 wherein the hydrophobicadditive comprises hydroxyl-terminated polybutadiene, and the tin and/oramine catalyst(s) used promote the isocyanate-hydroxyl reactionpreferentially and are selected from the group consisting of UL22, Cotin222, 1,4-diazabicyclo[2.2.2]octane (dabco), and dibutyltin dilaurate(DBTDL) or the like and combinations thereof.
 54. A system according toclaim 36 wherein the preformed components provide one or more surfaceshaving attached thereto a biologically active agent selected from thegroup cytokines, hydroxyapatite, growth factors, autologous growthfactors, collagen or the like and combinations thereof.
 55. A systemaccording to claim 36 wherein the surface of one or more preformedcomponent(s) is provided or modified with reactive groups to promotetissue adhesion.
 56. A system according to claim 55 wherein the reactivegroups are covalently attached to the polymers used to fabricate thepreformed component(s), and are selected from amines, hydroxyl groups,or other reactive or hydrogen bonding functionalities.
 57. A systemaccording to claim 36 wherein the preformed component(s) are selectedfrom the group consisting of a) a single preformed component, b) aplurality of components adapted to be layered upon each other at thetissue site, c) a plurality of components adapted to be assembled at thetissue site in an interlocking fashion, such that the componentscooperate to provide a respective portion of the first and second majorsurfaces.
 58. A system according to claims 1 or 22 or 36 furthercomprising the use of one or more additional materials and/or stepsadapted to a) prepare the bone surface itself, b) provide a desiredinterface between bone, component(s), and/or the physiologicenvironment, and/or c) treat one or more surfaces of the component(s) inorder to provide them with different or improved properties as comparedto the inherent properties of the material providing the surface.
 59. Asystem according to claim 58 wherein the materials and/or steps areadapted to affect, improve or provide a surface property or functionselected from adhesion, lubricity, smoothness, conformance, tissuein-growth, or biocompatibility.
 60. A system according to claims 1 or 22or 36 wherein the system is adapted to be used for repairing a varietyof mammalian joints, including human joints selected from the groupconsisting of the tibial plateau of the knee, the acetabulum of the hip,the glenoid of the shoulder, the acromion process of the shoulder, theacromio-clavicular joint of the shoulder, the distal tibial surface ofthe ankle, the radial head of the elbow, the distal radius of theforearm, the proximal phalanx surface of the great toe, the proximalmetacarpal surface of the thumb, and the trapezium of the wrist.
 61. Asystem according to claim 60 wherein the system is adapted to be usedfor repairing the tibial plateau of the knee.
 62. A system according toclaim 60 wherein the system is adapted to be used for repairing theacetabulum of the hip.
 63. A system according to claim 13 wherein theimplant is provided in the form of a preformed knee implant preparedusing an ex vivo mold and having a first major surface adapted to bepositioned upon the tibial surface, and a second major surface adaptedto be positioned against the femoral condyle.
 64. A system according toclaim 63 wherein the second major surface is provided with a femoralglide path to facilitate its performance in situ.
 65. A system accordingto claim 64 wherein the glide path is in the form of a generally centraloval depression about 1 mm to about 5 mm deep at its lowest point andabout 30 mm to about 50 mm in length by 10 mm to 30 mm in width.
 66. Asystem according to claim 63 wherein the implant also includes a raisedtibial projection adapted to catch the posterior portion of the tibialplateau in situ.
 67. A system according to claim 63 wherein the implanthas dimensions on the order of between about 40 to about 60 mm in theanterior-posterior dimension, between about 30 mm to about 40 mm in themedial-lateral dimension, and a maximum thickness, at the posterior lip,of between about 10 mm and about 20 mm.
 68. A system according to claim63 wherein the preformed component includes ancillary means for securingthe component once formed in the joint site.
 69. A system according toclaim 68 wherein the ancillary means comprise one or more protrusionsadapted to be attached to either soft tissue and/or bone at the jointsite to improve fixation.
 70. A system according to claim 68 wherein thecontoured surface of the preformed component further comprises a contourhaving one or more protrusions, integral with the preformed component,and formed during the ex vivo molding process.
 71. A system according toclaim 70 wherein the protrusions are adapted to be integrated into thepreformed component during the ex vivo molding process and comprisesutures and/or fibrous biomaterials integrally formed with the componentitself.
 72. A system according to claim 68 wherein the ancillary meansare selected from the group consisting of adhesives, sutures, pins,staples, screws, and combinations thereof.
 73. A system according toclaim 70 wherein the implant is preformed in a mold having an anteriorcup edge that is substantially perpendicular to the plane of the cupitself, and a posterior mesial edge that is tapered and raised toaccommodate the corresponding shape of the tibial spine.
 74. A systemaccording to claim 73 wherein the mold is adapted to permits control ofsizing, conformance to the joint site, implant thickness and angularcorrection.
 75. A system according to claim 74 where the implant assumesa generally kidney-shaped configuration, adapted to correspond with thetibial surface, and provides a posterior mesial edge portion having anindentation to accommodate the typical shape of the corresponding tibialspine.
 76. A system according to claim 15 wherein the polyurethanecomprises an isocyanate selected from the group consisting of aromatic,aliphatic and arylakyl diisocyanates, and combinations thereof.
 77. Asystem according to claim 76 wherein the isocyanate is selected from thegroup consisting of toluene diisocyanates, naphthalene diisocyanates,phenylene diisocyanates, xylylene diisocyanates, diphenylmethanediisocyanates, cyclohexane diisocyanates, cyclohexyl-bis methylenediisocyanates, isophorone diisocyanates and hexamethylene diisocyanates.78. A system according to claim 63 further comprising a patella-femoraljoint form suitable adapted to be formed to, and held against, thefemoral bone surface, in order to permit the delivery of curablebiopolymer between the form and the bone.
 79. A system according toclaim 1 wherein the implant is provided in the form of a preformed kneeimplant prepared using an ex vivo mold and having a first major surfaceadapted to be positioned upon the tibial surface, and a second majorsurface adapted to be positioned against the femoral condyle, theimplant also includes a raised tibial projection adapted to catch theposterior portion of the tibial plateau in situ, the implant hasdimensions on the order of between about 40 to about 60 mm in theanterior-posterior dimension, between about 30 mm to about 40 mm in themedial-lateral dimension, and a maximum thickness, at the posterior lip,of between about 10 mm and about 20 mm, the preformed component includesancillary means for securing the component once formed in the jointsite, and the preformed component is fabricated from a polyurethane thatcomprises an isocyanate comprising a phenylene diisocyanate.